Avoid race in test

client_test.go

@@ -873,10 +873,14 @@ func testDownloadCancel(t *testing.T, ps testDownloadCancelParams) {
 	assert.True(t, new)
 	psc := leecherGreeting.SubscribePieceStateChanges()
 	defer psc.Close()
-	leecherGreeting.DownloadAll()
+
+	leecherGreeting.cl.mu.Lock()
+	leecherGreeting.downloadPiecesLocked(0, leecherGreeting.numPieces())
 	if ps.Cancel {
-		leecherGreeting.CancelPieces(0, leecherGreeting.NumPieces())
+		leecherGreeting.cancelPiecesLocked(0, leecherGreeting.NumPieces())
 	}
+	leecherGreeting.cl.mu.Unlock()
+
 	addClientPeer(leecherGreeting, seeder)
 	completes := make(map[int]bool, 3)
 values:

t.go

@@ -152,6 +152,10 @@ func (t *Torrent) deleteReader(r *reader) {
 func (t *Torrent) DownloadPieces(begin, end int) {
 	t.cl.mu.Lock()
 	defer t.cl.mu.Unlock()
+	t.downloadPiecesLocked(begin, end)
+}
+
+func (t *Torrent) downloadPiecesLocked(begin, end int) {
 	for i := begin; i < end; i++ {
 		if t.pieces[i].priority.Raise(PiecePriorityNormal) {
 			t.updatePiecePriority(i)
@@ -162,6 +166,10 @@ func (t *Torrent) DownloadPieces(begin, end int) {
 func (t *Torrent) CancelPieces(begin, end int) {
 	t.cl.mu.Lock()
 	defer t.cl.mu.Unlock()
+	t.cancelPiecesLocked(begin, end)
+}
+
+func (t *Torrent) cancelPiecesLocked(begin, end int) {
 	for i := begin; i < end; i++ {
 		p := &t.pieces[i]
 		if p.priority == PiecePriorityNone {